The research described in this proposal will employ an animal model, the laboratory rat, to investigate the effects of various forms of malnutrition on lactation performance. Initially, studies will be limited to the malnutrition imposed by simple food restriction; later experiments will include deficits of specific nutrients. Malnutrition will be imposed prior to pregnancy, during pregnancy, during lactation, during repeated reproductive cycles spaced at varying intervals, and during combinations of these treatments. The characteristics of lactation performance to be evaluated under these treatment conditions will include: the duration of lactation; the volume and composition of the milk produced, including both major and minor components; maternal body composition and nutritional status; the efficiency of the lactation process; and neonatal growth, body composition, and nutritional status. Available methodology suitable for use in small laboratory species will be employed. Standardized conditions for milk collection will be used to eliminate variability. Nutritioal status will be characterized by hematocrit, the concentrations of hemoglobin and serum albumin, and appropriate measures in blood and liver for the assessment of riboflavin, vitamin A, and iron nutriture.